PPs were rare in the EXTEND-maintained ileum, resulting in reduced B cell abundance in EXTEND-maintained lambs. (A) Control terminal ileum from 128 days’ gestational age has many organized lymphoid follicles. (B) Terminal ileum from a lamb that spent 111 days in utero and 28 days in EXTEND (total gestation 139 days) has few PPs (none visible in this section). (C) Quantitative analysis confirms dramatic reduction in PPs in the EXTEND-maintained terminal ileum. Each dot indicates mean PP counts from 1 lamb (3 cross-sections analyzed for each). (D) Cells staining positive for the B cell marker CD21 as a percentage of total cells staining for CD45 within peripheral blood mononuclear cells (MNC), terminal ileum, and prescapular lymph node cells. (E) Representative FACS plots showing decreased B cell populations in EXTEND-maintained MNC, terminal ileum, and lymph nodes. Percentages for these representative plots are recorded in the upper right-hand corner of each. ∗P < .05, ∗∗∗P < .001, ∗∗∗∗P < .0001.